KR20080001382A - Circuit for controlling data output - Google Patents

Abstract

A data output control circuit is provided to select a DLL(Delay Locked Loop) clock used in domain crossing by detecting a clock frequency during DLL off operation. A delay locked loop(100) outputs a first clock by delaying an external clock in response to a control signal. A phase detection part(200) outputs a detection signal by detecting a frequency of the external clock in response to the control signal. A decoder part(300) outputs a selection signal by decoding the detection signal. A delay part(400) outputs a second clock by delaying the first clock or by inverting and delaying the phase of the first clock in response to the selection signal.

Description

Data output control circuit {CIRCUIT FOR CONTROLLING DATA OUTPUT}

1 is a block diagram of a conventional data output control circuit;

FIG. 2 is a timing diagram illustrating a domain crossing operation when a low frequency clock is input and a DLL is turned on in the data output control circuit of FIG. 1.

3 is a timing diagram illustrating a domain crossing operation when a high frequency clock is input and a DLL is turned on in the data output control circuit of FIG. 1.

4 is a timing diagram illustrating domain crossing operations when a low frequency clock is input and a DLL is turned off in the data output control circuit of FIG.

5 is a timing diagram illustrating a domain crossing operation when a high frequency clock is input and a DLL is turned off in the data output control circuit of FIG. 1.

6 is a block diagram illustrating a data output control circuit according to an embodiment of the present invention;

7 is a block diagram illustrating a configuration of the phase detector of FIG. 6;

8 is an exemplary circuit diagram of the pulse generator of FIG.

9 is an exemplary circuit diagram of an edge delay signal determination unit of FIG. 7;

10 is a timing diagram for describing a phase detection operation of the phase detection unit of FIG. 7;

11 is an exemplary circuit diagram of a decoder unit of FIG. 6;

12 is a timing diagram showing a domain crossing operation when a low frequency clock is input and a DLL is turned on in the data output control circuit of FIG. 6;

FIG. 13 is a timing diagram illustrating a domain crossing operation when a high frequency clock is input and DLLdl is turned off in the data output control circuit of FIG. 6.

The present invention relates to a semiconductor memory device, and more particularly, to a data output control circuit for controlling data output.

In general, a DRAM (DRAM) is a volatile memory device including a plurality of cells including one transistor and one capacitor.

Synchronous DRAM has a multi-bank and pipelined data path structure, whose state is determined by commands according to control signals (/ CAS, / RAS, / WE, etc.) and operates in synchronization with the system clock. By doing so, high speed operation is realized.

Such a synchronous DRAM has a read access time (tAA) from a memory cell to a data output control block (TAA) during a read operation, and the DRAM uses an external clock using cas latency. Synchronize and output the data output.

Meanwhile, the DRAM generates an output enable signal OUTEN to output data after a read command according to a clock according to CAS latency (CL). The output enable signal generator generates an output enable signal OUTEN by latching a read command signal input in synchronization with an external clock, that is, a domain crossing operation, that is, a DLLCLK.

1 is a block diagram of a conventional data output control circuit. Referring to FIG. 1, the read command signal READ is delayed by tCMD through the read generator 10 and output as the internal read command RDCMD. In the DLL on operation, the DLL 20 generates the DLLCLK through negative delay of the clock CLK, and the delay unit 30 generates the FDLLCLK in which the phase of the DLLCLK is inverted and inverted. 40). Therefore, the output enable signal generator 40 can always perform a domain crossing operation with a half tCK margin.

On the other hand, during the DLL off operation, the DLL 20 generates the DLLCLK through the positive delay of the clock CLK, and the delay unit 30 generates the output enable signal generator by generating the FLLDLCK in which the phase of the DLLCLK is inverted. Output to (40). In this case, the output enable signal generator 40 may not obtain an appropriate domain crossing margin, and thus a domain crossing error may occur.

A case in which a domain crossing error may occur through a timing diagram illustrating a domain crossing operation of the output enable signal generator 40 will be described in more detail.

First, a case in which the DLL is turned on and operated will be described with reference to FIGS. 2 and 3. FIG. 2 is a timing diagram illustrating a domain crossing operation when a low frequency clock is input and a DLL is turned on in the data output control circuit of FIG. 1, and FIG. 3 is a domain diagram when a high frequency clock is input and a DLL is turned on in the data output control circuit of FIG. 1. A timing diagram showing the crossing behavior.

Referring to FIGS. 2 and 3, when the DLL is turned on and operated, even when a high frequency clock is input, it is understood that a normal domain crossing operation is performed in the same manner as when a low frequency clock is input. That is, the output enable signal generator 40 may latch the RDCMD signal at the rising edge of FDLLCLK with a margin of half tCK. This is because the delay unit 30 compensates for the delay tCMD of the RDCMD and the negative delay of the DLL 20, and generates a FDLCLK inverting the phase of the DLLCLK to secure a margin of the domain crossing operation.

Next, a case in which the DLL is turned off and does not operate will be described with reference to FIGS. 4 and 5. 4 is a timing diagram illustrating a domain crossing operation when a low frequency clock is input in the data output control circuit of FIG. 1 and the DLL is turned off, and FIG. 5 is a domain diagram when a high frequency clock is input in the data output control circuit of FIG. 1 and the DLL is turned off. A timing diagram showing the crossing behavior.

Referring to FIGS. 4 and 5, it can be seen that a domain crossing error may occur when a high frequency clock is input, unlike when a low frequency clock is input when the DLL is off and does not operate. That is, the output enable signal generator 40 does not secure an appropriate domain crossing margin when a high frequency clock is input, unlike a low frequency clock. Thus, a domain crossing error occurs.

When the low frequency clock is input, even if the DLL 20 is turned off to have a positive delay, the domain crossing error does not occur because there is a sufficient margin of pulse width for domain crossing. However, when the high frequency clock is input, when the DLL 20 is turned off, the clock eats only a positive delay, and thus cannot compensate for the delay (tCMD) of the RDCMD. Will occur.

Here, the cross point refers to a point where timing margin disappears between the time when the RDCMD is enabled and the rising edge of the FDDLCLK. If a cross point occurs, an error occurs in the process of latching the RDCMD to FDLLCLK, and the enable timing of the output enable signal is inadequate, resulting in a data fail.

Accordingly, an object of the present invention is to solve the above problems, and an object of the present invention is to detect a clock frequency during a DLL off operation and to select a DLL clock used for domain crossing.

In order to achieve the above object, the present invention provides a delay lock loop for delaying an external clock in response to a control signal DLLOFF and outputting it to the first clock DLLCLK, and detecting a frequency of the external clock in response to the control signal. A phase detection unit outputting the detection signal DET, a decoder unit decoding the detection signal, and outputting the detection signal as a selection signal, and delaying the first clock or reversing the phase in response to the selection signal. DLLCLKD).

Here, the delay lock loop outputs a positive delay to the first clock when the control signal is enabled, and outputs the first clock by negatively delaying the external clock when the control signal is disabled. It is preferable.

The control signal may be generated by a mode register set command and determined by an address bit input together with the mode register set command.

In addition, the phase detector outputs a result of determining the level state of the edge delay signal which delayed the edge of the external clock for a predetermined period of the external clock as the detection signal, and operates when the control signal is enabled. Do.

The phase detector may further include: an edge signal generator configured to generate a first edge signal synchronized with a first rising edge of the outer clock and a second edge signal synchronized with a second rising edge of the outer clock, and delaying the first edge signal. Delay means for generating at least one edge delay signal, an edge delay signal determining unit for generating the detection signal according to a level state of the edge delay signal in response to the second edge signal, and the external clock in response to the control signal And clock transmission means for selectively transmitting to the edge signal generator.

The edge signal generator may further include a first edge signal generator configured to generate a first edge signal transitioned to a first edge of the external clock and a first edge signal in phase with the first edge signal. Selectively transfers a first edge signal to a transfer gate, a first latch to latch and output a first edge signal received from the transfer gate, and receives a first edge signal from the transfer gate, And a second edge signal generator for generating a second edge signal transitioned in synchronization with a second edge, and a second latch for latching and outputting the second edge signal.

The delay means may include a plurality of unit delay units connected in series, and generate a plurality of edge delay signals in which delay amounts are sequentially increased through the unit delay units.

In addition, the edge delay signal determining unit outputs a detection signal according to the level state of the edge delay signal when the second edge signal is in the "high" level state.

The edge delay signal determination unit may generate a detection signal for judging the external clock at high frequency when the edge edge signal of the plurality of edge delay signals is high in the state where the second edge signal is in the high level. It is preferable.

The edge delay signal determining unit may generate a detection signal for determining the external clock as a low frequency when the edge edge signal of the plurality of edge delay signals is high among the plurality of edge delay signals. It is preferable.

The edge delay signal determination unit may include a delay signal determination unit corresponding to the edge delay signal, and the delay signal determination unit may include a first PMOS transistor, a second PMOS transistor, and a first PMOS transistor connected in series between a power supply voltage and a ground voltage. An NMOS transistor and a second NMOS transistor.

In addition, the edge delay signal is input to the gate of the first PMOS transistor and the second NMOS transistor, and the second edge signal inverted by the inverter is input to the gate of the second PMOS transistor, and the first NMOS transistor is gated. Preferably, the second edge signal is input to.

In addition, the decoder unit receives a signal decoded from the detection signal determined to be a low frequency and outputs a polling output gate to output a polling selection signal, and a signal decoded to detect the detection signal determined to be a high frequency signal to enable and output the rising select signal. It includes a rising output gate.

The present invention may further include an internal lead command generation unit for delaying a read command and outputting the internal read command, and an output enable signal generation unit for generating an output enable signal by latching the internal lead command to a rising edge of the second clock. Include.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

6 is a block diagram illustrating a data output control circuit according to an exemplary embodiment of the present invention. Referring to FIG. 6, a data output control circuit according to an exemplary embodiment of the present invention may include a delay locked loop 100, a phase detector 200, a decoder 300, a delay unit 400, and an internal command generator. 500 and an output enable signal generator 600.

The delay lock loop 100 generates a DLLCLK for synchronizing data to an external clock CLK. The delay lock loop 100 outputs an external clock having a negative delay in the on state to the DLLCLK, and outputs an external clock having the positive delay in the off state to the DLLCLK. Here, the negative delay means a delay in consideration of the delay until the data is output through the internal circuit, and the positive delay means a delay naturally occurring through the internal circuit.

The delay lock loop 100 may be turned on or off by the DLLOFF signal generated by the EMRS command. The state of the DLLOFF signal is preferably determined according to the state of the address bit input with the EMRS command.

The phase detector 200 determines whether the external clock CLK is a high frequency clock by determining the level state of the edge delay signal that has delayed the edge of the external clock CLK during one period of the external clock CLK. The detection signal DET <0: 2> is output. The phase detection unit 200 preferably operates when the DLLOF signal is enabled, that is, when the delay lock loop 100 is turned off and does not operate.

Here, the high frequency clock refers to a frequency clock that is larger than a frequency clock in which an error occurs because the domain crossing margin is not secured when the domain crossing operation is performed, that is, when the internal read command is latched with an external clock having a positive delay while the delay lock loop is turned off. .

The decoder 300 decodes the detection signal DET <0: n> to enable and output the rising select signal RDLL or the polling select signal FDLL. In the present embodiment, n will be described by way of example.

The delay unit 400 outputs the DLLCLK by delaying or inverting the phase of the DLLCLK in response to the rising select signal RDLL or the polling select signal FDLL. More specifically, if the rising select signal RDLL is enabled when the delay lock loop 100 is turned off, the delay unit 400 delays the DLLCLK having a positive delay and outputs the DLLCLKD, and the polling select signal FDLL is enabled. If it is, the phase of the DLLCLK having a positive delay is reversed and output to DLLCLKD. Since the configuration of the delay unit 400 can be easily implemented by those skilled in the art from the description of the delay unit 400 using the transfer gate, the inverter, the delay means, and the like, the detailed description is omitted.

The internal command generation unit 500 delays the input read command READ by tCMD and outputs the internal read command RDCMD.

The output enable signal generator 600 latches the enabled internal read command RDCMD to the rising edge of the DLLCLKD to generate the output enable signal OUTEN. The output enable signal OUTEN may be used as a signal for outputting data in synchronization with the external clock CLK.

7 is a block diagram illustrating a configuration of the phase detector of FIG. 6. Referring to FIG. 7, the phase detector 200 includes an edge signal generator 210, a delay unit 220, an edge delay signal determiner 230, and a clock transfer unit 240.

The edge signal generator 210 outputs a first edge signal P0 synchronized with the first rising edge of the external clock CLK and a second edge signal P1 synchronized with the second rising edge of the external clock CLK. do.

The delay means 220 delays the first edge signal P0 through a plurality of unit delay units connected in series to generate a plurality of edge delay signals A, B, and C in which the delay amount is sequentially increased. In the present embodiment, the unit delay unit will be described by exemplifying the case of the first delay unit 222, the second delay unit 224, and the third delay unit 226.

The edge delay signal determining unit 230 generates detection signals DET <0: 2> according to the level of the edge edge signals A, B, and C in response to the second edge signal P1.

The clock transfer means 240 selectively inputs the external clock CLK to the edge signal generator 210 in response to the DLLOF signal.

8 is an exemplary circuit diagram of an edge signal generator of FIG. 7. Referring to FIG. 8, the edge signal generator 210 may include a first edge signal generator 212, a transfer gate 214, a first latch 213, a second edge signal generator 216, and a second edge signal generator 216. A latch 217.

The first edge signal generator 212 generates a first edge signal P0 that transitions to "low" in synchronization with the first rising edge of the external clock CLK. More specifically, the first edge signal generator 212 may receive the data terminal D and the first edge signal, which are fed back to the output signal inverted through the clock terminal C and the inverter INV receiving the external clock CLK. And a D flip-flop having an output terminal Q for outputting (P0). Preferably, the output terminal of the first edge signal generator 212 is initialized to a "high" state.

The transfer gate 214 selectively outputs the first edge signal P0 to the second edge signal generator 216 in response to the first edge signal / P0 inverted from the first edge signal P0. .

The first latch 213 latches and outputs the first edge signal P0 transmitted from the transfer gate 214. The first latch 213 may include two inverters in which an input terminal and an output terminal are connected to each other.

The second edge signal generator 216 receives the first edge signal P0 as a data signal. The second edge signal P1 transitions to "low" in synchronization with the second rising edge of the external clock CLK. More specifically, the second edge signal generator 216 may include a clock terminal C for receiving the external clock CLK, a data terminal D for receiving the first edge signal P0, and a second edge signal P1. It includes a D flip-flop having an output terminal (Q) for outputting.

The second latch 217 latches and outputs the second edge signal P1. The second latch 217 may include two inverters in which an input terminal and an output terminal are connected to each other.

9 is an exemplary circuit diagram of an edge delay signal determining unit of FIG. 7. Referring to FIG. 9, the edge delay signal determination unit 230 includes a delay signal A determination unit 232, a delay signal B determination unit 234, and a delay signal C determination unit 236.

The delay signal A determination unit 232 has a configuration in which the second edge signal P1 detects the level state of the edge delay signal A in the "high" level state and outputs the detected state as the detection signal DET <0>.

More specifically, the delay signal A determination unit 232 includes a first PMOS transistor P1, a second PMOS transistor P2, a first NMOS transistor N1, and a first PMOS transistor connected in series between a power supply voltage and a ground voltage. Two NMOS transistors N2. The edge delay signal A is input to the gates of the first PMOS transistor P1 and the second NMOS transistor N2. The second edge signal P1 inverted by the inverter INV is input to the gate of the second PMOS transistor P2, and the second edge signal P1 is input to the gate of the first NMOS transistor N1. The delay signal A determination unit 232 preferably further includes a latch 233 for latching and outputting the detection signal DET <0>.

The operation of the delay signal A determination unit 232 will be described below. First, when the edge edge signal A is at the "low" level state while the second edge signal P1 is at the "high" level state, the first PMOS transistor P1, the second PMOS transistor P2, and the first NMOS transistor N1. ) Is turned on and the second NMOS transistor N2 is turned off. Accordingly, the second PMOS transistor P2 outputs a "high" level signal, and the latch 233 inverts the phase of the "high" level signal to output a detection signal DET <0> having a "low" level. That is, when the edge delay signal A is in the "low" level state while the second edge signal P1 is in the "high" level state, the detection signal DET <0> of the "low" level is output.

Next, when the edge delay signal A is at the "high" level state while the second edge signal P1 is at the "high" level state, the first PMOS transistor P1 is turned off, whereas the first NMOS transistor N1, The second NMOS transistor N2c is turned on. Accordingly, the first NMOS transistor N1 outputs a signal of the "low" level, and the latch 233 inverts the phase of the "low" level signal to output the detection signal DET <0> of the "high" level. . That is, when the edge delay signal A is in the "high" level state while the second edge signal P1 is in the "high" level state, the detection signal DET <0> of the "high" level is output.

The delay signal B determining unit 234 and the delay signal C determining unit 236 may output the detection signals DET <1> and DET <2> through the same configuration and operation as the delay signal A determining unit 232. . In addition, in the present exemplary embodiment, the edge delay determination unit 230 includes three delay signal determination units 232, 234, and 236, but the present invention is not limited thereto and may be extended according to the number of edge delay signals. .

10 is a timing diagram for describing a phase detection operation of the phase detection unit of FIG. 7. Referring to FIG. 10, first, a process of determining, by the phase detector 200, the external clock CLK as a low frequency clock will be described. The edge signal generator 210 generates a first edge signal P0 that transitions to "low" in synchronization with the first rising edge of the external clock CLK. The delay unit 220 sequentially delays the first edge signal P0 through the unit first delay unit 222, the unit second delay unit 224, and the unit third delay unit 226. Signal A, edge delay signal B, and edge delay signal C are generated. The edge delay signal determination unit 230 determines the level of the edge delay signal A, the edge delay signal B, and the edge delay signal C when the second edge signal P0 is in the "high" level state. And a detection signal DET <0: 2> corresponding to "high".

That is, if the level of the edge delay signals A, B, and C which delayed the edge of the external clock CLK is "low", "low", "high" during one period of the external clock CLK, the external clock CLK Can be determined as a low frequency clock having a large pulse width.

Next, a process in which the phase detector 200 determines the external clock CLK as a high frequency clock will be described. Since the operation of the edge signal generator 210 and the delay means 220 is the same as the process of the phase detector 200 to determine the external clock CLK as low frequency, detailed description thereof will be omitted. The edge delay determining unit 230 determines the level of the edge delay signal A, the edge delay signal B, and the edge delay signal C when the second edge signal P1 is in the "high" level state. And a detection signal DET <0: 2> corresponding to "high".

That is, if the level of the edge delay signals A, B, and C which delayed the edge of the external clock CLK is "low", "high", "high" during one period of the external clock CLK, the external clock CLK Can be determined as a high frequency clock having a small pulse width.

11 is an exemplary circuit diagram of a decoder unit of FIG. 6. Referring to FIG. 11, the decoder unit 300 is determined as 2 ⁿ (n = 2) NAND gates ND1 to ND8 for NAND operation of the detection signals DET <0: n> of each level state, and is determined as a high frequency clock. Rising output gate (RND) for receiving the detection signal and NAND operation, and a falling output gate (FND) for NAND receiving the detection signal determined as a low frequency clock.

Here, the detection signal DET <0: 2> of each level state is

DET <0>, DET <1>, DET <2>; DET <0> DET <1> DETB <2>, DET <0> DETB <1> DET <2>,

DET <0> DETB <1> DETB <2>, DETB <0> DET <1> DET <2>, DETB <0> DET <1> DETB <2>,

DETB <0> DETB <1> DET <2> and DETB <0> DETB <1> DETB <2>. In addition, detection signals DET <0: 2> determined by the low frequency clock and detection signals <0: 2> determined by the high frequency clock are shown in Table 1 below.

DET <0> DET <1> DET <2> Judgment LOW LOW LOW Low frequency LOW LOW HIGH Low frequency LOW HIGH HIGH High frequency HIGH HIGH HIGH High frequency

Hereinafter, the operation of the decoder unit 300 will be described. When one of the detection signals determined to be low frequency is enabled, the polling output gate FND enables and outputs the polling select signal FDLL. When one of the detection signals determined to be high frequency is enabled, the rising output gate RND enables and outputs the rising select signal RDLL.

FIG. 12 is a timing diagram illustrating domain crossing operations when a low frequency clock is input and a DLL is turned off in the data output control circuit of FIG. 6. As described above, the delay unit 400 inverts the phase of the DLLCLK having the positive delay and outputs the inverted phase to the output enable signal generator 600 in response to the enabled poll selection signal FDLL.

In the case of a low frequency external clock, since the pulse width is large, the output enable signal generator 600 uses the DLLCLKD having an enable time and a constant margin of the internal read command RDCMD to latch the internal read command RDCMD. You can perform the operation.

FIG. 13 is a timing diagram illustrating a domain crossing operation when a high frequency clock is input and DLLdl is turned off in the data output control circuit of FIG. 6. As described above, the delay unit 600 delays the DLLCLK having the positive delay in response to the enabled rising select signal RDLL and outputs the delayed DLLCLK to the output enable signal generation unit 600.

Conventionally, when a high frequency external clock is input, a pulse width is small, and a cross point at which the enable edge of the internal lead command and the rising edge of the DLLCLK coincide during the domain crossing operation in which the output enable signal generator latches the internal lead command, According to the present exemplary embodiment, since the DLLCLK whose phase is inverted is output to the output enable signal generator 600 according to a frequency situation in which a positive delay is taken, a margin for stably performing a domain crossing operation can be secured.

That is, according to an exemplary embodiment of the present invention, when the fixed delay loop is turned off, not only the low frequency external clock is input but also the high frequency external clock is input, the domain crossing operation can be stably performed, thereby operating frequency of the semiconductor memory device. The area is widened.

As described above, the data output control circuit of the present invention can select the DLL clock used for domain crossing by detecting the clock frequency during the DLL-off operation, thereby ensuring stable output of data by securing an appropriate domain crossing margin even at low frequencies. It has the effect of making it possible.

In addition, preferred embodiments of the present invention are disclosed for the purpose of illustration, those skilled in the art will be able to various modifications, changes, additions, etc. within the spirit and scope of the present invention, these modifications and changes should be seen as belonging to the following claims. something to do.

Claims (17)

A delay lock loop outputting a first clock by delaying the external clock in response to the control signal; A phase detector for detecting a frequency of the external clock in response to the control signal and outputting a detection signal; A decoder to decode the detection signal and output a selection signal; A delay unit delaying the first clock or reversing the phase in response to the selection signal to output a second clock; Data output control circuit comprising a. The method of claim 1, wherein the delay lock loop, When the control signal is enabled, the external clock is positively delayed to output the first clock. Data output control circuit. The method of claim 2, wherein the delay lock loop, Outputting the first clock by negatively delaying the external clock when the control signal is disabled Data output control circuit. The method of claim 2 or 3, wherein the control signal, Determined by mode register set command and address bit Data output control circuit. The method of claim 1, wherein the phase detection unit, Outputting, as the detection signal, a result of determining the level state of the edge delay signal having delayed the edge of the external clock for a predetermined period of the external clock; Data output control circuit. The method of claim 5, wherein the phase detection unit, Operating when the control signal is enabled Data output control circuit. The method of claim 6, wherein the phase detection unit, An edge signal generator for generating a first edge signal synchronized with the first rising edge of the outer clock and a second edge signal synchronized with the second rising edge of the outer clock; Delay means for delaying the first edge signal to generate at least one edge delay signal; An edge delay signal determining unit configured to generate the detection signal according to the level state of the edge delay signal in response to the second edge signal; And clock transmission means for selectively transmitting the external clock to the edge signal generator in response to the control signal. Data output control circuit. The method of claim 7, wherein the edge signal generator, A first edge signal generator configured to generate a first edge signal transitioned in synchronization with a first edge of the external clock; A transfer gate for selectively intermitting the transfer of the first edge signal in response to the inverted first edge signal in phase with the first edge signal; A first latch for latching and outputting a first edge signal received from the transfer gate; A second edge signal generator which receives a first edge signal from the transfer gate and generates a second edge signal transitioned in synchronization with a second edge of the external clock; And a second latch configured to latch and output the second edge signal. Data output control circuit. The method of claim 7, wherein the delay means, Including a plurality of unit delay unit connected in series Data output control circuit. The method of claim 9, wherein the delay means, Generating a plurality of edge delay signals, the delay amount of which is sequentially increased through the unit delay unit Data output control circuit. The method of claim 10, wherein the edge delay signal determination unit, Outputting a detection signal in accordance with the level state of the edge delay signal by the second edge signal; Data output control circuit. The method of claim 11, wherein the edge delay signal determination unit, When the second edge signal is in the "high" level state, if there are many edge delay signals in the "low" level state among the plurality of edge delay signals, a detection signal for determining the external clock at high frequency is generated. Data output control circuit. The method of claim 12, wherein the edge delay signal determination unit, Generating a detection signal for determining the external clock as a low frequency when there are many edge delay signals in the "high" level state among the plurality of edge delay signals when the second edge signal is in the "high" level state; Data output control circuit. The method of claim 11, wherein the edge delay signal determination unit, A delay signal determination unit corresponding to the edge delay signal, wherein the delay signal determination unit includes a first PMOS transistor, a second PMOS transistor, a first NMOS transistor, and a second NMOS transistor connected in series between a power supply voltage and a ground voltage. Containing Data output control circuit. The method of claim 14, wherein the first PMOS transistor and the second NMOS transistor, The edge delay signal is input to the gate, the second edge signal inverted by the inverter is input to the gate of the second PMOS transistor, and the second edge signal is input to the gate of the first NMOS transistor. Data output control circuit. The decoder of claim 13 or 14, wherein the decoder unit is A falling output gate that receives a signal decoded by the detection signal determined to be a low frequency and outputs a polling selection signal and a rising output gate that receives a signal decoded by the detection signal determined to be a high frequency and enables a rising select signal to be output. Containing Data output control circuit. The method of claim 1, An internal command generator for delaying a read command and outputting the internal read command; An output enable signal generator configured to latch the internal read command to a rising edge of the second clock to generate an output enable signal Data output control circuit further comprising.

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